1. Field of the Invention
The present invention relates to an engine air intake apparatus and particularly to an air intake apparatus in which an air intake passage is configured integrally on an air cleaner.
2. Description of the Related Art
In passenger car engines, air intake noise emitted from air intake passage inlet portions accounts for a large share of overall noise during slow running when noise resulting from mechanical operation and vibration of the engine itself, exhaust noise, etc., are comparatively small. Thus, one important task has been to reduce the air intake noise during slow running while ensuring sufficient intake air flow required during high-speed operation to avoid reductions in engine power.
In view of these conditions, in some conventional engine air intake apparatuses, air suction portions are constituted by: a normally-open suction port having an aperture area that is constant; and a variable suction port having an aperture area that changes, and the aperture area of the variable suction port is changed depending on the rotational frequency of the engine so as to be increased when the engine is in a high rotational frequency range and reduced or closed in a normal rotational frequency range. (See Patent Literature 1, for example.)
Other conventional engine air intake apparatuses include: a first duct having one end open to atmospheric air, including a flow control portion that is closed at low rotational frequencies, and opened at high rotational frequencies; and a second duct open to atmospheric air that is longer than the first duct. (See Patent Literature 2, for example.)
Patent Literature 1: Japanese Utility Model Laid-Open No. SHO 63-60072 (Gazette)
Patent Literature 2: Japanese Patent Laid-Open No. HEI 07-27028 (Gazette)
Because these conventional engine air intake apparatuses include two independent passages constituted by a normally-open air intake passage and an air intake passage having a changing aperture area, the size of the air intake apparatuses is increased. Thus, some problems have been that demand for reductions in mounting space for the air intake apparatus inside engine compartments accompanying demands for increased auxiliary machinery and reductions in size and weight cannot be met, and the weight of parts is increased.